Pool Not Opened in 2 Years - Vinyl Liner Stained & Sagging

Hello everyone, this is my first post and I apologize in advance for all of the questions ...

I recently purchased a home that had been neglected by the previous owner. The 18 x 36 T Shaped Vinyl IGP had not been opened for over 2 years. I managed to get things running last week, but the pool is in poor condition. The pool has about 1/4 inch of mud covering the entire bottom of the pool and the walls are stained black. As of today the PH is about 7.2 and the chlorine is between .75 and 1.0 (Taylor K-2006 kit is being shipped). I recently realized that my in-line automated chlorinator (Hayward CL-200) is not functioning, so I've been using bleach and liquid chlorine to raise the level. I'm trying to get as much stuff off the bottom as possible with a mesh leaf rake, and started vacuuming today on waste, but it's very slow going.

My questions and concerns are about the deep dark staining on the vinyl liner, can these be removed? I've read some threads suggesting Ascorbic Acid can remove organic dark stains. Can anyone provide comments on this?

Also, the liner is sagging down from the coping in a few places. I've read that using a heat gun or boiling water the liner can be stretched back into the track on the coping? Is this something best left to a professional? And Finally :-) What vinyl liner patch adhesive is recommended?

Thanks everyone!

Hey again:)

I think you need to address getting the pool clean and the liner back into it's track before you worry about any possible staining.

Organic stains will lift from the chlorine you add, metal stains will require ascorbic acid (or similar), but you need to start with a clean and functional pool before messing with the stains.

Pool is online and functioning, water is clear after replacing the filter manifold. I now need to remove the vinyl liner stains. Vitamin C works great against the stains directly, I now want to use ascorbic acid to treat the entire pool, walls, etc... Is there a link to detailed instructions? I have seen links to generic ascorbic acid, is that recommended? Also, I have read it needs to be used in conjunction with PolyQuat 60. If these instructions are written out somewhere, please point me to that link. Thank you.

Filter is DE, Vinyl, approximately 42K Gallons.

Thanks in advance.